I'm not sure about which books you may have read in the past but for an overview of the war I've found Stephen Turnbull's "Samurai Invasion: Japan's Korean war" to be a good starting point to get a high level grasp. The author comes from a japanese military history background and the book is understandably biased towards the military side of the war (as opposed to say the minutae at the various courts) that but at the same time he draws from both korean and japanese sources.

Just as importantly, his book doesn't pretend to be more than it is. The other two works you might come across on the war, Samuel Hawley's "The Imjin War: Japan's Sixteenth-Century Invasion of Korea and Attempt to Conquer China" and Kenneth Swope's "A Dragon’s Head and a Serpent’s Tail: Ming China and the First Great East Asian War, 1592-1598" draw a lot of criticism for exactly the opposite. Full review of the two works here, and my comment would be that I agree with the criticisms of Hawley from my own reading of that book.

If you're already across the overview of the war and are more serious about it then:

• Jingbirok ("The book of corrections") by Ryu Seong Ryung. Ryu was the prime minister of korea prior and during the war. He wrote this work as an post-mortem of the war and his perspective on what could've been done better.

• Nanjung Ilgi ("War diary of Yi Sun Shin") by Yi Sun Shin.

Both works give insights into the characters of two key players from the korean side.